Comparisons of Rigid Proctoscopy, Flexible Colonoscopy, and Digital Rectal Examination for Determining the Localization of Rectal Cancers

BACKGROUND: Rigid proctoscopy is considered essential for rectal tumor localization, although the current gold standard for detection of colorectal cancers is colonoscopy. The European Society for Medical Oncology Guidelines indicate that rigid and flexible endoscopies afford essentially identical results, although little evidence is yet available to support this. OBJECTIVE: The purpose of this study was to determine the accuracy of colonoscopy in identifying the location of rectal cancer and to compare the results with those of rigid proctoscopy and digital rectal examination. DESIGN: This was a retrospective analysis of a prospective database. SETTINGS: The study was conducted at a single tertiary colorectal surgery referral center. PATIENTS: A total of 173 patients scheduled for curative surgery for histologically verified rectal adenocarcinoma between December 2009 and February 2015 were entered into the study, after having given informed consent. MAIN OUTCOME MEASURES: The main study measure was the mean difference and limits of agreement in assessment of the height of the distal edge of rectal cancer from the anal verge, using the Bland and Altman method. RESULTS: The mean difference between rigid proctoscopy and flexible colonoscopy was -0.2 cm (95% CI, -2.0 to 1.6 cm). The mean difference between rigid proctoscopy and digital rectal examination was 0.3 cm (95% CI, 1.9 to 2.4 cm). Intermethod variability larger than the 95% CI between rigid and flexible endoscopes was correlated to the tumor height (OR, 4.27 (95% CI, 1.84-3.10); p = 0.021). LIMITATIONS: This study was conducted in a single center. CONCLUSIONS: The limits of agreement (-2.0 and 1.6 cm) in identifying the height of rectal cancers from the anal verge are sufficiently small to support the view that flexible colonoscopy provides similar tumor locations to those measured by rigid proctoscopy, although the discrepancy occasionally exceeded 2 cm for tumors >5 cm above the anal verge.